Many quinolone derivatives are known to exhibit high antibacterial activities(see U.S. Pat. Nos. 4,670,444, 4,795,751 and 5,631,266). However, some of the conventional quinolone compounds have limited activities against Gram-positive bacteria, while other quinolone derivatives exhibit the problem of poor water-solubility and bioavailability or side effects such as high cytotoxicity.
The present inventors have, therefore, endeavored to develop non-toxic compounds having the higher potency against the broad spectrum of bacteria; and have unexpectedly found that certain quinolone carboxylic acid derivatives having a pyridylpyrrolidine moiety at the 7-position of the quinolone nucleus exhibit the broad spectrum antibacterial activity and the reduced cytotoxicity.